Research: Photoinduced dynamics and momentum distribution of chiral charge density waves

In daily life, "chirality" is most intuitively illustrated by our left and right hands—mirror images that cannot be perfectly overlapped. In condensed matter physics, chirality is also a fundamental property, but dynamically controlling chiral states in quantum materials has long been a challenge. In most systems, chirality is locked by the crystal lattice, leaving little room for external tuning.

The layered material 1T-TiSe₂ has recently drawn attention as a platform for a new kind of chirality: a chiral charge density wave (CDW), where electrons collectively arrange to break inversion symmetry and give rise to handedness within an otherwise achiral lattice. Previous optical experiments hinted at light-induced chiral responses in this material, but the microscopic mechanism and its connection to the CDW remained elusive.

To resolve this puzzle, a research team employed time-resolved X-ray diffraction (trXRD) with circularly polarized laser pulses to capture ultrafast snapshots of the CDW. Their experiments revealed a striking ~20% difference in CDW suppression depending on whether left- or right-handed circularly polarized light was used. Moreover, they observed momentum-resolved circular dichroism from chiral domains, directly linking chirality to the underlying CDW order. Remarkably, the laser excitation also led to an immediate increase in CDW correlation length, signaling the photoinduced expansion of chiral domains.

This work not only clarifies the mechanism behind light-driven chirality in TiSe₂, but also demonstrates that trXRD with circularly polarized pumps provides a powerful method to probe and manipulate chiral states. The findings open up exciting possibilities for using ultrafast light pulses to dynamically control chirality in quantum materials.

Q. Qiu, Sae H. Chun, J. Park, D. Jang, L. Yue, Y. Kim, Y. Ahn, M. Jho, K. Han, X. Jiang, Q. Xiao, T. Dong, J.-Y. Ji, N. Wang, J. van den Brink, J. van Wezel, Y. Peng,
Photo-induced Dynamics and Momentum Distribution of Chiral Charge Density Waves in 1T-TiSe₂,
Phys. Rev. Lett. 135, 116904 (2025) (arXiv)